An FA (Factory Automation) environment system (FA system) includes a plurality of devices and a plurality of networks. The FA system includes devices such as a sensor, a robot, and a servomotor, and controllers that control these devices, for example. The FA system also includes plural networks such as an inter-controller network for sharing information among the controllers, an information network for sharing information among PCs (Personal Computers) and the controllers, a field network designed to connect the devices in a coordinated manner in real time, and a servo network designed to provide communication with higher speeds and higher reliability than in the field network to connect the devices faster.
Typical communication methods of the information network include Ethernet (registered trademark)/IP (Internet Protocol) and PROFInet, and typical communication methods of the inter-controller network includes MELSECNET and FL-net. The field network has typical communication methods such as CC-Link (Control & Communication Link) and Devicenet, and the servo network has typical communication methods such as SSCNET (Servo System Controller Network).
Among these methods, the field network and the servo network require high-speed and high-reliability communication as characteristics of the FA system. An industrial robot is cited as an example of the devices that configure the FA system. The industrial robot is operated through servo amplifiers and servomotors according to commands issued from a controller to execute operations such as expansion, contraction, bend, stretch, upward or downward movement, leftward or rightward movement, and turn. Two or more servo amplifiers and servomotors are sequentially operated in a predetermined procedure to realize complicated operations of the industrial robot.
An operation of a machine tool called “roll feeder” is explained as an example of the industrial robot. In the roll feeder, a feeder moves forward a roll placed on a base by adjusting the speed and a punch press descends at a position where the roll stops, thereby performing punching. In this example, a method is used in which instructions are issued from a controller through servo amplifiers to servomotors that drive the feeder moving the roll and the punch press performing punching, respectively. When precise machining is to be performed with respect to X, Y, and Z axes, a high-accuracy coordinated operation is required. Accordingly, synchronous communication between the controller and each servo amplifier or servomotor is periodically established to realize concurrent activation or high-accuracy coordinated operations among plural servos. To realize the high-accuracy coordinated operations, highly reliable communication needs to be performed.
Meanwhile, as a technique that provides highly reliable communication in a master/slave system, Patent Literature 1 mentioned below describes a technique that enables to, when there is no response from a slave to a wired bus network, detect abnormal communication and enter an operation mode at abnormal time in which the slave is disconnected, for example.